Noncorrosive aqueous solutions



Patented Sept. 15, 1936 UNITED STATES PATENT OFFICE NONCORROSIVE AQUEOUS SOLUTIONS No Drawing. Application April 11, 1935,

. Serial No. 15,820

12 Claim.

This invention relates to noncorrosive aqueous solutions and methods for preparing the same and more particularly to aqueous alcoholic solutions particularly adapted for use in heat exchange devices such as cooling systems of internal combustion engines.

Heat exchange devices, particularly the cooling systems of internal combustion engines are composed of three essential parts:

(1) A metal heat exchanger,

(2) A liquid for transferring the excess heat of the engine to the atmosphere, and

(3) A mechanism for circulating the liquid in the heat exchanger.

The heat exchanger consists of a hot portion such as the engine block made of ferrous metals, where the heat is tranferred from the engine to the liquid; and a cold portion, or the radiator usually made of copper-bearing metals, where the heat is transferred from the liquid to the atmosphere.

Assuming that the cooling system is of correct design and in good working condition, it is necessary for its continued eflicient operation that: (1) The cooling liquid be able to function immediately,

(2) The metal heat exchanger be kept intact,

(3) The overall coefficient of heat transfer be maintained substantially at its original value, and

(4) The course of circulation of the liquid must be kept unobstructed.

Water is the cooling liquid most commonly em- .ployed, but its use in cold weather is condemned by its tendency to solidify at a relatively high temperature. Therefore, it has become corrmion I practice to replace the water with an anti-freeze liquid. Such an anti-freeze liquid comprises water and a freezing point depressant. There are two groups of freezing point depressants which are commonly employed. One common type of freezing point depressant is the highly soluble electrolytes, such as calcium chloride, sodium lactate and the like. mother commonly employed type of freezing point depressant is the water soluble non-electrolytes, such as methanol, ethanol, ethylene glycol, glycerol and the like.

It is well known that water alone and aqueous solutions of the various freezing point depressants have a corrosive action on the metals employed in the heat exchange devices. While the aqueous solutions of the non-electrolyte freezing point depressants are not as corrosive as the solutions of the electrolyte freezing point depressants, they are more corrosive than water alone. This corrosive action of the aqueous heat exchange liquids in situ on the metal sin'face which decreases the 10 coefllcient of heat transfer of the heat exchanger, and (4) the accumulation of the corrosion. products in the circulation conduits which tends to suppress the required movement of the cooling liquid in the heat exchanger.

There have been many attempts to overcome these difficulties. So far, the only practicable method of overcoming these difficulties has been to incorporate, in the antifreeze liquids, materials which will form a film on the metal surfaces protecting such surfaces from the corrosive action of the liquids. However, these methods have not proved to be entirely satisfactory for the reason that the film forming materials will prevent the corrosion of only one metal in the system at the expense of the other metals. Since the ferrous metals are the most subject to corrosion, it has been the practice generally to employ a material which will prevent the corrosion of such metals. When such a .corrosion inhibitor is employed, the corrosion of copper bearing metals and the like becomes greater than in the absence of such corrosion inhibitor. Accordingly, it is apparent that the problem involved cannot be considered to be satisfactorily solved unless the corrosion of all of the metals of the heat exchanger is inhibited.

Some of the corrosion inhibitors heretofore employed have the further disadvantage that they form an insulating film on the metal thereby greatly decreasing the coeflicient of heat transfer of the heat exchange device. This is an undesirable result.

An object of the present invention is to provide an aqueous heat exchange liquid which is noncorrosive or substantially non-corrosive to all of the metals of a heat exchanger such as ferrous metals, copper bearing metals, tin, aluminum and the like. A further object is to provide an antifreeze liquid, employing a non-electrolyte freezing point depressant, which liquid is substantially non-corrosive to the heat exchanger as a whole. A further object is to provide a method for preparing such liquids. Still further objects are to provide new compositions of matter and to ading disulfides.

'va'nce the art. Other objects will appear hereinlafter.

These objects may be accomplished in accordance with our invention which comprises incorporating, in water or an aqueous solution of a non-electrolyte freezing point depressant such as methanol, ethanol, ethylene glycol, glycerol and the like and in the absence of substantial amounts of electrolyte, at least 0.03% oi. a nitrite of a metal above aluminum in the electromotive series together with a small amount or a member or the group comprising mercapto-aryl-thiazoles, hydrocarbon mercaptans and their correspond- The nitrite employed is preferably that of an alkali metal such as sodium and potassium. The mercapto compounds which have proved to be most effective are the mercaptoarylenethiazoles such as mercapto benzothiazole and the long chain alkyl mercaptans, such as lauryl and cetyl mercaptans. Of these, the mercapto-arylene thiazoles appear to be the most efllcient.

We have found that such an aqueous liquid is substantially non-corrosive to all of the metals of the usual heat exchange devices, particularly such as employed inthe cooling systems of internal combustion engines, and does not materially affect the heat transfer coemlcient of the device. This will be more readily apparent from the following Table I which shows the effect of a 40% solution by weight of CD-10 alcohol in ordinary hydrant water employed by itself and containing the various ingredients. (JD-10 alcohol is completely denatured alcohol prepared in accordance with the indicated Govermnent formula.

Table I Corrosion: mg./s

in./l hrs. q Inhibitor Iron Brass None 33 l. Sodium nitrite 0.1% 0. 3 8. 0 l-mercapto benzothiazole 0.01% 37 1. 4 Sodium nitrite 0.l%+i-mercapto benzothiazolo 0.01% 0. 8 0. 3

The corrosion experiments, the results of which are given in the above and in the following tables were made by immersing properly cleaned metal strips in the alcohol solution at 82 C. under air-saturated conditions. The corrosion data are expressed in milligrams of metal lost per square inch of 'surface area exposed per 100 hours of exposure, abbreviated mg./sq. in./100 hrs.

In the above experiments, the iron and brass were in contact. It will be noted that the sodium nitrite clearly decreased the corrosion of the iron, whereas the corrosion of the brass was clearly increased. On the other hand, the mercapto-benzothiazole had substantially no efiect on either the iron or the brass. dium nitrite and mercapto benzothiazole were employed together, the corrosion of both the iron and the brass was very greatly decreased.

At least 0.03% of sodium nitrite, based on the solution, must be employed. Much less than this amount of the sodium nitrite will accelerate corrosion of the iron. More than 0.03% of sodium nitrite may be employed. Larger amounts of sodium nitrite will increase the protection of the metal. In practice, amounts up to about When the so- 1.00% will be employed. Larger amounts may be employed, if desired, but without any material advantage. The efiect oi. varying amounts of sodium nitrite will be apparent from the following Table II:

Table II Corrosion: mg./sq. in./ Cone. of NaN0| on 100 wt. oi Iron Brass Percent From the above table,it will be apparent that, when the sodium nitrite is employed alone in an eiTective amount, the corrosion of the brass is. clearly increased.

The amount of the sulphur compound or mercaptan may be varied from a mere trace up to about 1%. In practice, it is desirable to employ from about 0.0005 gm. per sq. in. of brass in the heat exchange device up to about 0.01 gm. per sq. in. of brass. Larger amounts than these may be employed but without advantage. In practice the amounts of the mercapto compounds will be varied up to about 1%. However, about 0.01% will be sufiicient for most automobile radiators. The efiject of varying the amount of mercaptobenzo thiazole in our liquid is shown by the following Table III:

Table III Cone. of Corrosion: mgJsq. in./ mercapto- 100 hrs. benzothiazole on wt. 01 solution Iron Brass Percent The solution employed in the test in the abovev Table IV Corrosion: mg./s in./l00 hrs. q N itrites Iron Brass Control (n0 inhibitor) 33 l. 5 Sodium nitrite 0. 3 8. 6 Calcium nitrite (average of two) 0. 8 5. 0 Magnesium nitrite 1. l 6. 9 Barium nitrite 0.6 7. 0

Other marcaptans may be employed in place of the mercapto benzothiazoles, such as the aryl mercaptans, aralkyl mercaptans, cyclo alkyl mercaptans, alkyl mercaptans and particularly the While we have disclosed the preferred embodilong chain alkyl mercaptans. While the low molecular weightmercaptans will be eflective,they are undesirable 'due to their volatility and objectionable odor. Also, the corresponding disulfides may be employed. The efl'ect of some of the mer-' captans and disulfldes is shown in the following table V in which the concentrations are 0.01% by weight in a 40% alcohol solution containing 0.1%

While the mercapto benzothiaaole appears to be the most eifective inhibitor, according to these tests, the other compounds are also very effective. In general, the disulfides are less effective than the corresponding mercaptans.

A formula which has proven to be very effective and satisfactory when employed in automobile radiators was prepared as follows:

To commercial ethanol, denatured according to formula CD40, was added 0.25% by weight of commercial sodium nitrite, either in the solid form or as a concentrated water solution, and 0.025%

by weight of a trade grade of mercapto benzothiazole, known as Captax". The inhibited alcohol, when diluted with water to give from 20 to 40% by weight of alcohol, was found to be substantially noncorrosive to iron, brass and the other metals such as copper, aluminum, solder and brazing compounds and did not materially aflect the emciency of the radiators. I

Among the nitrites, those of the following metals are the most desirable: Sodium, potassium, barium, strontium, calcium and magnesium.

.Among the mercaptans and disulfldes which will be found to be suitable, the following may be mentionedz' Mercapto benzothiazole and its homologues such as the mercapto tolylthiazoles, mercapto xylylthiazoies, mercapto ethylbenzothiazoles, and mercapto naphthothiazoles; also thio-' phenols, thiocresols, dimercapto benzenes, thionaphthols, benzyl mercaptans, methyl benzyl mercaptans, cyclohexyl mercaptan; long chain alkyl mercaptans such as lauryl mercaptan, cetyl mercaptan and the like and the corresponding disulfldes.

By the term long chain alkyl mercaptans",

mean those containing 8 or more carbon Although undiluted alcohol is much less corrometal containers used to transport and store it.

. By the term non-electrolyte freezing point depressants as employed herein andinthe claims,

we mean the water soluble mono and polyhydric aliphatic alcohols whichdecrease the freezing point of water when dissolved therein. By the term "substantial amounts of electrolytes, we mean amounts of over 5% by weight of the solution.

ments of our invention and the preferred modes of carrying the same into efiect, it will be readily apparent to those skilled in the art that many variations and modifications may be made therein without departing from the spirit of our invention. Accordingly, the scope of our invention is to be limited solely by the appended claims construed as broadly as is permissible in view of .the prior art.

We claim:

1. A non-corrosive liquid suitable for use in heat exchange devices and the like containing iron and copper-bearing metals which comprises water having incorporated therein at least 0.03% of a nitrite of a metal above aluminum in the electrc- V motive series and a small amount of a member of the group consisting of mercapto arylene thiazoles,.hydrocarbon mercaptans and the corresponding disulfldes. in the absence of substantial amounts of electrolytes.

2. A non-corrosive liquid suitable for use in heat exchange devices and the like containing iron and copper-bearing metals which comprises water having incorporated therein at least 0.03% of an alkali metal nitrite and a small amount of a member f th group consisting of mercapto arylone thiazoles, hydrocarbon mercaptans and the corresponding disulfldes, in the absence of substantial amounts of electrolytes.

3. A non-corrosive liquid suitable for use in heat exchange devices and the like containing iron and copper-bearing metals which comprises water having incorporated therein at least 0.03% of an alkali metal nitrite and a small amount of a mercapto arylene thiazola, in the absence of substantial amounts of electrolytes.

4. A non-corrosiye liquid suitable for use in heat exchange devices and the like containing long chain alkyl mercaptan, in the absence of substantial amounts of electrolytes.

5. A non-corrosive liquid suitable for use in heat exchange devices and the like containing iron and copper-bearing metals which comprises water having incorporated therein at least 0.03% of sodium nitrite and a small amount of a member of the group consisting of mercapto arylene thiazoles, hydrocarbon mercaptans and the corresponding disuliides, in the absence of substantial amounts of electrolytes.

6. A non-corrosive liquid suitable for use in heat exchange devices and the like containing iron and copper-bearing metals which comprises water having incorporated therein at least 0.03% of a nitrite of a metal above aluminum in the electromotive series and'a small amount of a mercapto benzothiazole; in the absence of substantial amounts of electrolytes.

'7. A non-corrosive liquid suitable for use in heat exchange devices and the like containing iron and copper-bearing metals which comprises water having incorporated therein at least 0.03% of an alkali. metal nitrite and a small amount of a mercapto benzothiazole, in the absence of substantial amounts of electrolytes.

of sodium nitrite and a small amount of a mercapto benzothiazole, in the absence of substantial amounts of electrolytes.

9. A non-corrosive liquid suitable for use in heat exchange devices and the like containing iron and copper-bearing metals which comprises Water having incorporated therein a non-electrolytefreezing point depressant and at least 0.03% of a nitrite of a metal above aluminum in the electromotive series and a small amount of a member of the group consisting of mercapto arylene thiazoles, hydrocarbon mercaptans and the corresponding disulfldes, in the absence of substantial amounts of electrolytes.

10. A non-corrosive liquid suitable for use in heat exchange devices and the like containing iron and copper bearing metals which comprises water having incorporated therein at least 0.03% of sodium nitrite and a small amount of mercapto benzc thiazole in the absence of substantial amounts of electrolytes.

11. A non-corrosive liquid suitable for use in heat exchangeldevices and the'like containing iron and. copper bearing metals which comprises water having incorporated therein at least 0.03% of calcium nitrite and a small amount of mercapto benzo thiazole in the absence of substantial amounts of electrolytes.

12. A non-corrosive liquid suitable for use in heat exchange devices and the like containing iron and copper bearing metals which comprises water having incorporated therein at least 0.03% of sodium nitrite and a small amount of cetyl mercaptan in the absence of substantial amounts of electrolytes.

RICHARD G. CLARKSON. CHARLES J. PEDERSEN.

CERTIFICATE OF CORRECTION.

Patent No. 2,054,282.

the above numbered patent requiring correction as follows: column, line 51-, for the word "Nitrates" read Nitrites; and that the said September 15, 1936.

RICHARD G. CLARKSON, ET AB.

It is hereby certified that error appears in the printed specification of Page 2, second Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 8th day of December, A. D. 1956',

(Seal) Henry Van Arsdaie Acting Commissioner of Patents. 

